Technical Field
The present invention relates to an engine starting apparatus.
Related Art
A typical engine starting method includes using an inertia-engagement-type starter to turn an engine at a low engine speed (of 400 rpm or less) and then igniting or injecting fuel into a combustion chamber, thereby increasing an engine speed to an idle speed only through combustion in the combustion chamber.
However, since such a method increases the engine speed from a low engine speed range to the idle speed with combustion alone, an amount of fuel to be injected when starting the engine has to be increased, resulting in deterioration of fuel economy.
FIG. 12 shows a relationship Z of an engine speed and a fuel injection quantity of a gasoline engine with a fixed accelerator position. A required fuel injection quantity at and near the idle speed Na of the engine is specified by the relationship Z while, below the predetermined engine speed Nmin (about 450 rpm), the required fuel injection quantity non-linearly increases away from the relationship Z as the engine speed is decreased. That is, below the predetermined engine speed Nmin, a fuel injection quantity increased above an injection quantity specified by the relationship Z (referred to as an increased injection quantity) is required.
A range of engine speeds less than the predetermined engine speed Nmin is referred to as a range I. A range of engine speeds equal to or greater than the predetermined engine speed Nmin is referred to as a range II, where the engine speed can be maintained without increasing the injection quantity.
A conventional method for starting the engine with the inertia-engagement-type starter requires, to turn the engine at an engine speed in the range I, the injection quantity to be increased above the injection quantity specified by the relationship Z, which may diminish the fuel economy.
Therefore there is a need for a technique for starting the engine, which increases the engine speed to approximately the idle speed Na prior to fuel injection so that increasing the injection quantity is not required when starting the engine, thereby improving the fuel economy.
Such a technique for starting the engine may employ an electrical motor and generator referred to as an integrated starter and generator (ISG), or a motor generator (MG).
However, the ISG and the MG suffer from expensiveness. In addition, since they are alternators, start-up performance is poor relative to the inertia-engagement-type starter incorporating therein a direct-current (DC) motor.
It would therefore be desirable to have a technique for starting the engine that increases the engine speed to approximately the idle speed Na prior to the fuel injection with an inexpensive inertia-engagement-type starter having good start-up performance. However, the inertia-engagement-type starter produces large cranking noise. Conventionally, it is therefore necessary to undergo combustion before the engine speed reaches the range II as above and terminate driving the starter.
Without eliminating or reducing the discomfort caused by the cranking noise, it is impossible to have a technique for starting the engine with the inertia-engagement-type starter, which has improved fuel economy.
Japanese Patent Application Laid-Open Publication No. 2002-188549 discloses a technique for starting the engine by increasing the engine speed up to the idle speed with the inertia-engagement-type starter. However, no cranking noise is taken into account. In addition, in the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2002-188549 and the conventional technique for starting the engine that increases the engine speed within a low engine speed range, a one-way clutch isolates transfer of torque of a starter motor to the engine at the same as or after the ignition in the combustion chamber. That is, cranking the engine is terminated at the same time as or after the ignition in the combustion chamber.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing an engine starting apparatus capable of starting an engine via an inexpensive inertia-engagement-type starter while improving fuel economy.